Tanning of leather or hides with mineral tanning agents



Patented Aug. 23, 1938 UNITED STATES PATENT OFFICE TANNING OF LEATHER OR HIDES WITH MINERAL TANNING AGENTS Germany No Drawing. Application June 13, 1936, Serial No. 85,124. In Germany June 25, 1935 8 Claims.

The present invention relates to the tanning of leather or hides with mineral tanning agents. When leather or hides are tanned with mineral tanning agents there is frequently obtained leather which does not fufil the desired requirements of fullness and feel. Furthermore, in the case of chrome tanning which is the most usual process individual colouring, which is frequently undesired, often occurs, and avoidance of this individual colouring in the case of chrome tanning has already been a long considered problem.

According to the present invention there is provided a process of tanning leather and hides with solutions of trivalent chromium or iron salts, characterized by the incorporation in the tanning lye of one or more higher molecular albumen cleavage products.

In the presence of these higher molecular albumen cleavage products the tanning process is different in an important respect from processes in which these substances are absent. Apparently the mineral salts, e. g. the chromium salts and the higher molecular albumen cleavage products form complex compounds, the characteristic indication of this being the immediate change of colour'and the fact that the limit for flocculation upon the addition of alkaliis shifted.

, In the process according to the invention, that is with the addition of higher molecular albumen cleavage products, the tanning lye can safely be rendered considerably more basic than is otherwise usual, so that it is possible to avoid the swelling phenomena usual in the case of tanning with iron salts, and in the case of tanning with complex chromium compounds to obtain an absolutely neutral leather.

Leathers obtained in accordance with the present invention are considerably stronger than those obtained in the usual way, without loss of soft- 40 ness. The leathers tanned with complex chromium compounds have a light grey to white colour which is readily removed in the dyeing process.

In order that the invention may be well understood the following examples are given by way of example:

Example 1.Strongly limed and drenched calves hides are pickled and then tanned within 8 hours with a 6/12 basic chromium lye, obtained 50 by boiling together a commercial chrome tanning salt with albumen cleavage products, in the ratio of ClzOa albumen cleavage products=1:8.35.- After the tanning the leather is neutralized, greased. (fatliquored), and if desired dyed to a light colour. The tanned leather is practically white, and if the leather is dyed the absence of the undesired green ground colour is noticeable.

Example 2.Pickled and pressed out goats hide is tanned slowly with ten times the amount of a 1% chrome alum solution, to which during boiling there is added 1.5 to 3% of albumen cleavage products of the type of lysalbinic and protalbinic acids, the whole being rendered basic by the addition of sodium carbonate solution. The leathers are rinsed for a short time and greased. Contrary to the usual process of tanning with chrome alum the amount of sodium carbonate added for rendering the lye basic can be increased to 1.6 to 1.9 times the amount which can be added without flocculation occurring in the absence of the substances forming complex salts. It is thus possible to obtain as a result of the tanning process itself a leather of neutral or even weakly alkaline reaction of very bright colour and strong grain, and to omit any subsequent neutralizing step.

Example 3.-11.kg. of iron ammonium alum, or the corresponding amount of another ferric salt, in 330 litres of'water are dissolved and the solution added at 30 C. to 33 kg. of a solution of higher molecular albumen cleavage products neutralized with soda lye. The colour of the iron salt solution changes from yellow to red. 80-90 kg. of pickled sheep skins are slowly tanned with the tanning lye thus obtained, the tanning lye being added gradually. When the tanning lye has all been added the leather is rendered more basic and at the same time neutralized by the ad.- dition of 10 kg. of a 10% sodium carbonate solution; The tanned leather is rinsed and greased and after dressing provides a good liming leather.

We claim:

1. A method for the preparation of a tanning lye consisting of the step of adding higher molecular albumen cleavage products to tanning metal compounds selected from the group of trivalent chromium and iron salts, the amount of said albumen cleavage products being at least eight times that of said tanning metal compounds.

2. A method for the preparation of a tanning lye consisting of the step of adding higher molecular abumen cleavage products of the type of lysalbinic and protalbinic acids to tanning metal compounds selected from the group of trivalent chromium and iron salts, the amount of said albumen cleavage products being at least eight times that of said tanning metal compounds.

3. A tanning lye containing tanning metal compounds selected from the group of the trivalent chromium and iron salts, and at least one higher chromium and iron salts, and at-least one higher molecular albumen cleavage product of the type of lysalbinic and protalbinic acids, the amount or said albumen cleavage product being at least eight times that of said tanning metal compounds, and said tanning lye being free from oxidizing agents.

5. A tanning lye containing tanning metal compounds selected from the group of the trivalent chromium and iron salts, at least one higher molecular albumen cleavage product, and a greater amount of alkali than the usual tanning lyes containing mineral salts, for rendering the tanning lye less acid than said usual tanning lyes, the amount of said albumen cleavage product being at least eight times that of said tanning metal compounds, and said tanning lye being free from oxidizing agents.

6. A tanning lye containing tanning metal compounds selected irom the group of the trivalent chromium and iron salts, at least one higher molecular albumen cleavage product of the type of lysalbinic and protalbinic acids, and a greater amount of alkali than the usual tanning lyes containing mineral salts, for rendering the tanning lye less acid than said usual tanning lyes, the amount of said albumen cleavage product being at least eight times that of said tanning metal compounds, and said tanning lye being free from oxidizing agents.

'7. A process for tanning leather or hides comprising the steps of using a tanning lye as claimed in claim 3 and maintaining the tanning lye less acid than the usual tanning lyes containing mineral salts.

8. A process for tanning leather. or hides comprising the steps of using a tanning lye as claimed in claim 4 and maintaining the tanning lye less acid than the usual tanning lyes containing mineral salts.

LUDWIG JABLONSKI. KURT LINDNER. 

